First - rock auto isn't a brand. For any given part there can be a wide range of options from high quality-high dollar to "chinese crap".

Second - Rock auto isn't a store like Summit or Auto-Zone. It is a clearing house website. So if you order 3 things, one might ship from summit, one from the manufacturer, and another from a auto parts store that is going out of business

The multi-source shipping is what can be a deal killer. Using that same example of three parts, unlike ordering from summit where it all goes in one discounted rate box, means you pay shipping for each part. I think there is a tool on the site that lets you check to try to get parts shipped from minimum number of sources if they happen to have them available.

All that said, I have used them but not often. Usually with shipping added in I get better deals from summit or amazon. Rock auto IS an amazing source for looking up part numbers, and researching options.